The present invention relates to a method for preparing transparent casting resins, prepared from aromatic diglycidyl ethers, carboxylic-acid anhydrides, metal salts of carboxylic acids and auxiliary agents and additives. The compounds are suitable particularly for the encapsulation of opto-electronic components.
It is known to use epoxy casting resins with a bisphenol A base which can be hardened with acid anhydride (DE-OS No. 1 589 264) for covering or encapsulating electronic components. A disadvantage of the known epoxy resin compounds of the bisphenol A/acid anhydride type, which are prepared using customary reaction accelerators such as tertiary amines, BF.sub.3 -amine complexes or other amine-containing compounds, is the relatively long setting time needed before components cast therewith can be removed from the mold. On the other hand, these amine-containing accelerators lead in a short time to a yellowish appearance of the molded materials at temperatures above 80.degree. C.
Casting resin compounds with a cycloaliphatic base which can be hardened by acid anhydrides for casting opto-electronic components also are known (DE-OS No. 2 642 465). While these resin compounds do not exhibit the disadvantages mentioned above in connection with the aromatic diglycidyl-ether resins, their mechanical properties are substantially poorer. Thus, they exhibit lower impact resistance and bending strength as well as insufficient adhesion to substrates. This brittleness has a particularly adverse effect on the temperature shock stress, tensile, impact and compression behavior of cast opto-electronic components. In some opto-electronic components, molded substances of such hardness influence the operation of sensitive chips, for example, by generating mechanical stresses.